Photovoltaic module

ABSTRACT

A photovoltaic module includes an encapsulated photovoltaic element and an infrared-transmissive decorative overlay simulating conventional roofing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of pending U.S. patent application Ser. No.12/811,493, filed on Jul. 1, 2010, which is a national stage 371application of International Application No. PCT/US2009/030253, filedJan. 7, 2009, which claims the benefit of U.S. Provisional PatentApplication No. 61/019,740, filed Jan. 8, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to photovoltaic modules, and in particularto photovoltaic modules adapted for installation on roofs.

2. Brief Description of the Prior Art

The use of photovoltaic (“PV”) modules on roofs is becoming increasinglycommon. Often perched on tile or shingle-covered roofs, these solarenergy-generating arrays are quite visible, and generally not quiteaesthetically pleasing to the eye, somewhat comparable to the TVantennas of the past. To date the installations appear to have beenmotivated by purely practical, functional considerations; theregenerally appears to be little to no color and design coordinationbetween the PV modules and the roofing tiles or shingles on which themodules are mounted.

PV modules usually feature a black to purple or blue surface protectedby a thin transparent glass or plastic cover. These colors frequently donot work well aesthetically with the rest of the roof.

Photovoltaic materials require incident light to produce energy via thephotoelectric effect. Such materials typically have a wavelengthdependency in their response to incident light. That is to say that someparts of the spectrum may be used by a PV module more effectively thanothers in producing electricity. Intuitively, to cover or color the PVmodule with an opaque material to obtain a desirable aestheticappearance would cause a blocking of the incident light and thephotovoltaic material would no longer be active. To color the topsurface with a clear coating, film or membrane may change the color, butmay not easily yield a desirable effect for a roofing product. Also, avisually transparent film may still block parts of the spectrumimportant for power generation.

A variety of approaches have been taken for using the substantial areaprovided by roofs to collect solar energy. One approach has been tocover existing roofs using systems employing panels, tiles or shinglesincluding solar cells. Panel-type systems are disclosed, for example, inU.S. Pat. No. 5,232,518 and U.S. Pat. No. 6,245,987.

Various attempts have been made to blend photovoltaic cells withtraditional roofing systems. For example, U.S. Pat. Nos. 5,437,735 and5,575,861, each incorporated herein by reference, disclose aphotovoltaic shingle system including a strip of roofing material havingan overlap portion, and tabs extending from the overlap portion. Each ofthe tabs includes a photovoltaic device. U.S. Pat. No. 6,875,914discloses a photovoltaic roofing system including photovoltaicpower-generating roofing shingles provided with a linearly alignedelectrical terminal. A protective cap shields the electricalconnections. U.S. Pat. No. 6,883,290 discloses a shingle systemincluding photovoltaic modules secured to a base to create a shingleassembly with a venting region between the module and the base fortemperature regulation. U.S. Pat. No. 6,928,775 discloses a multi-useelectric tile module for walling, flooring or roofing applications thatcan include a photovoltaic module. U.S. Patent Application PublicationNo. 2006/0000178 discloses a shingle assembly with a support bracketspecifically adapted for the installation of photovoltaic shingles.

U.S. Pat. No. 4,574,160 discloses a flexible, rollable photovoltaic cellmodule. U.S. Pat. No. 4,860,509 discloses photovoltaic cells incombination with single-ply roofing membranes.

U.S. Patent Application Publication No. 2005/0102947 disclosesphotovoltaic building materials having a regular shape, such asrectangular or trapezoidal, and carrying solar cells formed from thinfilm materials, conventional crystal/silica, or photoelectric silicaspheres. The materials are specially adapted for installation along theridgeline of a roof. U.S. Patent Application Publication No.2005/0144870 discloses a shingle system incorporating a photovoltaicmodule and a base to define a venting region, and may include awaterproofing element.

U.S. Patent Application Publication No. 2005/0178429 discloses flexibleintegrated photovoltaic roofing membrane shingles having a “dragon'stooth” shape with solar elements that connect electrically with previousand successive shingle courses. U.S. Patent Application Publication No.2005/0263179 discloses a photovoltaic module architecture which includeselectrical interconnects that provide for connecting the anode of onemodule with the cathode of another module.

U.S. Patent Application Publication No. 2005/0268962 discloses flexiblephotovoltaic cells and related systems. U.S. Pat. No. 6,729,081,incorporated herein by reference, discloses a self-adhesive photovoltaicmodule. U.S. Patent Application Publication No. 2006/0032527 discloses asolar panel overlay and assembly for mounting on an underlying roofdeck, designed to mimic the appearance of the underlying shingled roofdeck.

U.S. Patent Application Publication No. 2003/0121228 discloses adendritic web solar cell shingling system providing much thinnerphotovoltaic arrays than conventional cells.

U.S. Pat. No. 6,730,841 discloses a method and apparatus for mounting aflexible photovoltaic roofing material.

U.S. Patent Application Publication No. 2006/0042683 discloses a systemfor mounting photovoltaic cells on a surface and for using theelectrical energy produced. The cell can be pigmented to assureefficient collection of available radiation, for example, by using apink-colored glass.

U.S. Patent Application Publication No. 2005/0048821 discloses adye-sensitized solar cell having a high conversion efficiency.

U.S. Patent Application Publication No. 2003/0154973 discloses aradiation collector configured to collect incident radiation. Thecollectors can be colored to give the appearance of traditional shinglesor other roofing or building material such that the roof appearsaesthetically the same as a traditional roof.

U.S. Pat. No. 5,650,019 discloses a solar cell module having athree-layer structure including a thin film solar cell, a hard resinlayer such as polycarbonate to mechanically protect the solar cell, anultraviolet radiation absorbing adhesive layer to protect the hard resinlayer, such as ethylene vinyl acetate including an ultraviolet absorbersuch as a suitable benzophenone or triazole, and an outermost layerhaving excellent weatherability, such as a fluororesin.

U.S. Pat. No. 6,331,673 discloses an amorphous silicon solar cell modulein which the solar cell is encapsulated in a transparent organicpolymer, namely an acrylic resin and covered with a thin film of asuitable fluoropolymer resin, reinforced with glass fibers.

There is a continuing need for photovoltaic modules having morecontrollable and desirable aesthetics for use in roof applications whilestill maintaining sufficient efficiency in power generation.

SUMMARY OF THE INVENTION

The present invention provides a photovoltaic module comprising aphotovoltaic element having an upper surface, an encapsulant resin layerover the upper surface of the photovoltaic element, a decorative overlaypositioned above the upper surface of the photovoltaic element, and anoptional cover plate. The decorative overlay is preferably substantiallytransmissive of both near infrared radiation and infrared radiation.

Preferably, the decorative overlay is selected so that the operation ofthe photovoltaic element is not substantially inhibited. Preferably, theelectrical power output from the photovoltaic element is notsubstantially reduced by the presence of the decorative overlay.

In one presently preferred embodiment of the present invention, thedecorative overlay is positioned outside the optional cover plate. Inanother embodiment of the present invention, the decorative overlay ispositioned under the optional cover plate. In a further embodiment ofthe present invention, the decorative overlay is embedded in theencapsulant resin layer. In yet another embodiment of the presentinvention, the decorative overlay is positioned on top of theencapsulant resin layer.

Preferably, in one aspect the present invention provides a photovoltaicmodule wherein the decorative overlay simulates the appearance of aconventional roofing shingle surface. In another aspect, the presentinvention provides a photovoltaic module wherein the decorative overlaysimulates the appearance of a clay ceramic or cementitious roofing tile.In yet another aspect, the present invention provides a photovoltaicmodule wherein the decorative overlay simulates the appearance of apolymeric roofing or siding panel.

The decorative overlay can be provided in a number of different ways.For example, in one aspect, the decorative overlay comprises a coatinglayer or ink including a binder and at least one infrared-transmissivepigment. The coating layer or ink can be applied directly to theoptional cover plate of the photovoltaic module, directly on theencapsulant resin layer, or on an infrared-transmissive film.Preferably, the at least one infrared-transmissive pigment is selectedfrom the group consisting of nanoparticle titanium dioxide, zincsulfide, zinc oxide, CI Pigment Black 31, CI Pigment Black 32, CIPigment Red 122, and CI Pigment Yellow 13. Thus, the decorative overlaycan comprise a film material. In one aspect, the film material includesa carrier and at least one infrared-transmissive pigment. In anotheraspect, the film material includes a decorative layer formed on thesurface of the film. When the decorative layer is printed on the filmmaterial, the encapsulant resin layer, or the optional cover plate, thedecorative layer is preferably formed by a halftone printing process.

The present invention also provides a process for producing a decorativephotovoltaic module. In one embodiment, the process includes providing aphotovoltaic module including a semiconductor stack encapsulated in aninfrared-transmissive resin to form an encapsulant resin layer andoptionally covered with a top plate, and adhering an overlay filmbearing a decorative pattern to the encapsulant resin layer or optionaltop plate using an infrared-transmissive adhesive material. In anotherembodiment, the process of the present invention comprises providing aphotovoltaic module including a semiconductor stack encapsulated in aninfrared-transmissive resin to form an encapsulant resin layer andcovered with an optional top plate, and printing a decorative pattern onthe encapsulant resin layer or optional top plate using aninfrared-transmissive ink. In a further embodiment of the process of thepresent invention, the process comprises providing a photovoltaic moduleincluding a semiconductor stack encapsulated in a layer of aninfrared-transmissive resin to form an encapsulant resin layer, adheringan overlay film bearing a decorative pattern to the layer ofinfrared-transmissive resin, and optionally adhering a top plate to theoverlay film using an infrared-transmissive adhesive material.

In another aspect, the present invention provides a photovoltaic modulecomprising a photovoltaic element having an upper surface, anencapsulant resin layer over the upper surface of the photovoltaicelement, and a decorative overlay positioned above the upper surface ofthe photovoltaic element. In this aspect, the overlay is substantiallytransmissive of near infrared radiation and infrared radiation. In thisaspect, the decorative overlay can be positioned outside the encapsulantresin layer, under the encapsulant resin layer, or the decorativeoverlay can be embedded in the encapsulant resin layer. Preferably, thedecorative overlay simulates the appearance of a conventional roofingshingle surface, a conventional roofing tile or slate, or a conventionalmetal or polymeric roofing panel or siding panel.

In this aspect, the decorative overlay preferably comprises a coatinglayer including a binder and at least one infrared-transmissive pigment.Preferably, the at least one infrared-transmissive pigment is selectedfrom the group consisting of zinc sulfide, zinc oxide, nanoparticletitanium dioxide, CI Pigment Black 31, CI Pigment Black 32, CI PigmentRed 122, and CI Pigment Yellow 13. Preferably, the overlay comprises afilm material. Preferably, the film material includes a carrier and atleast one infrared-transmissive pigment. Preferably, the film materialincludes a decorative layer on the surface of the film. In oneembodiment of the photovoltaic module of the present invention, thedecorative layer is preferably formed by a halftone printing process.

In yet another aspect, the present invention provides a process forproducing a decorative photovoltaic module comprising providing aphotovoltaic module including a semiconductor stack encapsulated in aninfrared-transmissive resin having an upper resin layer, and adhering anoverlay film bearing a decorative pattern to the upper resin layer usingan infrared-transmissive adhesive material. Preferably, the decorativephotovoltaic module is incorporated into a roofing cover.

In another aspect, the present invention provides a process forproducing a decorative photovoltaic module comprising providing aphotovoltaic module including a semiconductor stack encapsulated in aninfrared-transmissive resin having an upper resin layer, and printing adecorative pattern on the upper resin layer using an ink selected fromthe group consisting of opaque inks, infrared-transmissive inks andpartially transmissive inks. Preferably, the decorative pattern furtherincludes an infrared-transmissive ink on at least a first portion of theupper resin layer and an opaque ink on at least a second portion of theupper resin layer. In one aspect of the present process, the decorativephotovoltaic module is preferably incorporated into a roofing cover.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic plan view showing a process for producing aphotovoltaic module according to the present invention and employing aninfrared-transmissive overlay film and a conventional photovoltaic cell.

FIG. 2 is a schematic plan view showing the process of FIG. 1,substituting an overlay film having a mottled appearance in the visiblerange but being substantially transmissive to near infrared and infraredradiation.

FIG. 3 is a schematic plan view showing a second process for producing amodified photovoltaic module according to the present invention, inwhich a design is printed on a conventional photovoltaic module using afour-color technique with ink pigmented to be absorbed in the visiblerange, but substantially transmissive to near infrared and infraredradiation, and optionally leaving some areas of the surface withoutcolor printed on the module.

FIG. 4 is a schematic sectional elevational view of a photovoltaicmodule of the prior art.

FIG. 5 is a schematic sectional elevational view of a first embodimentof a photovoltaic module of the present invention.

FIG. 6 is a schematic sectional elevational view of a second embodimentof a photovoltaic module of the present invention.

FIG. 7 is a schematic sectional elevational view of a third embodimentof a photovoltaic module of the present invention.

FIG. 8 is a schematic sectional elevational view of a fourth embodimentof a photovoltaic module of the present invention.

FIG. 9 is a schematic sectional elevational view of a fifth embodimentof a photovoltaic module of the present invention.

FIG. 10 is a schematic sectional elevational view of a sixth embodimentof a photovoltaic module of the present invention.

FIG. 11 is a schematic sectional elevational view of a seventhembodiment of a photovoltaic module of the present invention.

FIG. 12 is a schematic sectional elevational view of an eighthembodiment of a photovoltaic module of the present invention.

DETAILED DESCRIPTION

As used in the present specification and claims:

“Photovoltaic module” means one or more photovoltaic cells electricallyconnected to operate as an integral unit.

“Infrared radiation” means electromagnetic radiation having a wavelengthof from 1.4 micrometers to 1000 micrometers.

“Near infrared radiation” means electromagnetic radiation having awavelength of from 0.75 micrometers to 1.4 micrometers.

“Visible radiation” means electromagnetic radiation having a wavelengthof from 350 to 750 nanometers.

“Substantially transmissive” when referring to radiation means having anaverage transmission coefficient of at least 50 percent.

“Highly transmissive” when referring to radiation means having anaverage transmission coefficient of at least 80 percent.

In one aspect, the present invention provides improved photovoltaicmodules having surface colors that are aesthetically compatible withother types of roof coverings, such as previously installed shingles,tiles, slate, etc.

Solar radiation has substantial spectral components in the near infraredand infrared ranges. Preferably, the photovoltaic modules of the presentinvention include a color layer that is formulated to be substantiallytransmissive or transparent to the infrared portion of the spectrum,thus to permit photovoltaic modules to function while using the visibleportion of the spectrum to achieve a desired aesthetic effect.

Conventional solar cells can include several layers, such as an n-typesilicon layer doped with an electron donor such as phosphorous, orientedtowards incident solar radiation, and a p-type silicon layer doped withan electron acceptor, such as boron, as well as a pair of electricalcurrent conducting layers for interconnection with other cells and/orthe environment. The silicon layers can be embedded in a protectivelayer of encapsulant material, such as ethylene vinyl acetate, andcovered with glass. Antireflection coatings can be applied to theelectron-donor layer and the glass to maximize solar radiationadsorption. The antireflection coating gives the conventional solar cella characteristic blue or black appearance.

The present invention provides a photovoltaic module having controllableand desirable aesthetics for use in roof applications while stillmaintaining sufficient efficiency in power generation. The photovoltaicdevice of the present invention is provided with a coating or overlaylayer having a desirable visual appearance in the visible spectrum andsubstantial transmissivity in the near infrared and infrared regions ofthe electromagnetic spectrum. Portions of the visible spectrum areselectively absorbed so that the light reflected in the visible rangegives a desired color while the near infrared and infrared light, or atleast a substantial portion thereof, passes through the coating oroverlay to activate the photovoltaic device.

Referring now to the figures in which like reference numerals representlike elements in each of the several views, there is shown in FIG. 1 aschematic plan view of a process for producing a modified photovoltaicmodule 1 c according to the present invention and employing an infraredtransparent overlay film 1 b and a conventional photovoltaic module 1 aincluding a mono-crystalline silicon solar cell covered with a dark bluesilicon nitride antireflection film and available from China ElectricalEquipment Group, Nanjing, China. In the present process an overlay film1 b is placed over and adhered to the upper surface of a conventionalphotovoltaic module 1 a. The overlay film 1 b is transparent ortransmissive for radiation in the infrared and near-infrared portions ofthe spectrum, but includes a visible-light absorbing pigment to providea monochromatic appearance to the human eye. The film 1 b is bonded tothe upper surface of the conventional photovoltaic module 1 a using aninfrared light-transmissive adhesive (not shown), such as an ethylenevinyl acetate hot melt adhesive composition having a softening pointgreater than the anticipated operating temperature range for themodified photovoltaic module 1 c. Alternatively, the overlay film 1 bcan be placed over the conventional photovoltaic module 1 a and securedmechanically (not shown) to provide the modified photovoltaic module 1c.

FIG. 2 depicts the process of FIG. 1, except that an overlay film 2 bhaving a mottled appearance is substituted for the monochromatic overlayfilm 1 b employed in the process of FIG. 1. The overlay film 2 b has amottled appearance in the visible range but is substantially transparentto near infrared and infrared radiation. Application of the mottledoverlay film 2 b to a conventional photovoltaic module 2 a provides amodified photovoltaic module 2 c having a mottled appearance.

FIG. 3 depicts a further embodiment of a process for producing amodified photovoltaic cell according to the present invention. In thisembodiment, infrared-transmissive ink or coating material is applieddirectly to the copper nitride surface of the conventional photovoltaiccell. Four different inks, each having a different appearance in thevisible spectrum, but each being infrared andnear-infrared-transmissive, are applied as a pattern 3 b to the uppersurface of a conventional photovoltaic module 3 a using a suitabletechnique, such as a lithographic or ink-jet technique, to provide amodified photovoltaic module 3 c. The pattern can be a screenedstochastic half-tone pattern reproducing a color image, such as an imageof a section of a conventional roofing shingle covered with roofinggranules colored with conventional metal oxide colorants. For purposesof illustration, the individual color “dots” forming the pattern aredepicted as being large enough to be individually distinguishable to theunaided eye. However, a much finer screened pattern can be employed,such as one having a frequency of 30-200 lines per inch, to provide aconventional half-tone image. Optionally, one, two or more differentcolor inks or coating compositions can be used to form the color “dots.”Further, the pattern can exploit the preexisting colors of the othercomponents of the photovoltaic module to achieve a desired aestheticresult.

A conventional photovoltaic module 10 of the prior art is depicted inthe schematic sectional elevational view of FIG. 4. The photovoltaicmodule 10 includes a solar cell stack 12 formed from a plurality oflayers (not shown) including n-type and p-type crystalline,polycrystalline or amorphous silicon layers, transparent electrodelayers, and a backing plate, and fitted with external current collectingelectrodes 14 for connecting the solar cell stack to permit aphotocurrent to flow from the solar cell stack 12 to an external load(not shown). The solar cell stack 12 is encapsulated on its uppersurface (the surface intended to face the sun) by an outer layer ofupper surface encapsulant resin 16, and on its lower surface by an innerlayer 20 of lower surface encapsulant resin. The upper surfaceencapsulant resin is covered with a cover or top plate 18 transparent ortransmissive to infrared and near infrared radiation such as a suitableglass sheet or suitable fluororesin film, and the lower surfaceencapsulant resin layer 20 is covered by a backing plate 22 formed froma rigid material such as a rigid synthetic polymer composition such as anylon or polycarbonate or a metal such as aluminum.

A modified photovoltaic module 30 according to a first embodiment of thepresent invention is schematically illustrated in the sectionalelevational view of FIG. 5. The modified photovoltaic module 30 includesa solar cell stack 32 fitted with external current collecting electrodes34 for connecting the solar cell stack 32 to an external load. The solarstack 32 is encapsulated on its upper surface by an outer layer of uppersurface encapsulant resin 36, and on its lower surface by an inner layer40 of lower surface encapsulant resin. The upper surface encapsulantresin layer 36 is covered with a top plate 38, and the lower surfaceencapsulant resin layer 36 is covered by a backing plate 44. The uppersurface encapsulant resin layer 36 and the lower surface encapsulantresin layer 40 can be formed from the same resin material, or they canbe formed from different resin materials. However, the upper surfaceencapsulant resin layer 36 is preferably formed from a resin materialthat is substantially transparent or transmissive to both near infraredradiation and infrared radiation, such as an ethylene vinyl acetateresin. An infrared-transmissive overlay film 46 is adhered to the upperor outer surface of the top plate 38 by a thin film 48 ofinfrared-transmissive adhesive material. Optionally, theinfrared-transmissive overlay film 46 may itself be adherable withoutthe need for an additional thin film adhesive 48 (not shown). Theoverlay film 46 includes a surface coating 49 includingpigment-absorbing radiation in the visible range arranged in adecorative pattern, such as illustrated in FIG. 3 b. Surface coating 49can optionally be applied directly to top plate 38 (also not shown).

A modified photovoltaic module 50 according to a second embodiment ofthe present invention is schematically illustrated in the sectionalelevational view of FIG. 6. As in the case of the first embodiment ofthe modified photovoltaic module 30 illustrated in FIG. 5, the modifiedphotovoltaic module 50 of this second embodiment includes a solar cellstack 52 fitted with external current collecting electrodes 54 forconnecting the solar cell stack 52 to an external load. Further, thesolar stack 52 is encapsulated on its upper surface by an outer layer ofupper surface encapsulant resin 56, and on its lower surface by an innerlayer 60 of lower surface encapsulant resin. In addition, the lowersurface encapsulant resin layer 60 is covered by a backing plate 64.However, in this case, the upper surface encapsulant resin layer 56 iscovered with an infrared-transmissive overlay film 66, which in turn iscovered by a top plate 58. In this case, the infrared-transmissiveoverlay film 66 includes pigment-absorbing radiation in the visiblerange, dispersed in the overlay film 66 to give a mottled appearance tothe overlay film 66, such as illustrated in FIG. 1 b. The top plate 58is adhered to the overlay film 66 by a thin film 68 ofinfrared-transmissive adhesive material.

A modified photovoltaic module 70 according to a third embodiment of thepresent invention is schematically illustrated in the sectionalelevational view of FIG. 7. As in the case of the first embodiment ofthe modified photovoltaic module 30 illustrated in FIG. 5, the modifiedphotovoltaic module 70 of this third embodiment includes a solar cellstack 72 fitted with external current collecting electrodes 74 forconnecting the solar cell stack 72 to an external load. Further, thesolar stack 72 is encapsulated on its lower surface by an inner layer 80of lower surface encapsulant resin, and the lower surface encapsulantresin layer 80 is covered by a backing plate 84. However, in this case,the upper surface encapsulant resin layer 76 is formed from aninfrared-transmissive material including pigment absorbing radiation inthe visible range, dispersed randomly in the upper encapsulant resinlayer 76 to give a distinctive hue to the encapsulant resin layer 76,the hue being selected to match or complement the hue of a conventionalroofing shingle. The upper encapsulant layer 76 is in turn covered by atop plate 78.

A modified photovoltaic module 90 according to a fourth embodiment ofthe present invention is schematically illustrated in the sectionalelevational view of FIG. 8. As in the case of the first embodiment ofthe modified photovoltaic module 30 illustrated in FIG. 5, the modifiedphotovoltaic module 90 of this fourth embodiment includes a solar cellstack 92 fitted with external current-collecting electrodes 94 forconnecting the solar cell stack 92 to an external load. Further, thesolar stack 92 is encapsulated on its upper surface by an outer layer ofupper surface encapsulant resin 96, and on its lower surface by an innerlayer 100 of lower surface encapsulant resin. In addition, the uppersurface encapsulant resin layer 96 is covered with a top plate 98, andthe lower surface encapsulant resin layer 100 is covered by a backingplate 104. An infrared-transmissive overlay film 106 is adhered to theupper or outer surface of the top plate 98 by a thin film 108 ofinfrared-transmissive adhesive material. In another embodiment, theadhesive material is omitted, and the overlay film 108 is securedotherwise, such by suitable fasteners or edging material (not shown) tothe top plate 98. The upper surface of the overlay film 106 is providedwith a three-dimensional pattern simulating the appearance of roofinggranules on a conventional roofing shingle. The three-dimensionalpattern can be created by embossing, molding, selectively coating, or byany of the many ways known in the art for creating a three-dimensionalpattern. In addition, the overlay film 106 includes pigment-absorbingradiation in the visible range, providing a hue simulating the hue of aconventional roofing shingle.

A modified photovoltaic module 110 according to a fifth embodiment ofthe present invention is schematically illustrated in the sectionalelevational view of FIG. 9. As in the case of the first embodiment ofthe modified photovoltaic module 30 illustrated in FIG. 5, the modifiedphotovoltaic module 110 of this fifth embodiment includes a solar cellstack 112 fitted with external current collecting electrodes 114 forconnecting the solar cell stack 112 to an external load. The solar stack112 is encapsulated on its upper surface by an outer layer of uppersurface encapsulant resin 116, and on its lower surface by an innerlayer 120 of lower surface encapsulant resin. In addition, the lowersurface encapsulant resin layer 120 is covered by a backing plate 124.In this embodiment of the present invention, the upper surfaceencapsulant resin layer 116 is covered with an infrared-transmissiveoverlay film 126. The lower surface of the overlay film 126 is providedwith a three-dimensional pattern simulating the appearance of roofinggranules on a conventional roofing shingle. In addition, the overlayfilm 126 includes pigment that absorbs radiation in the visible range,providing a hue simulating the hue of a conventional roofing shingle.The upper surface of the overlay film 126 is covered with a top plate118, and adhered to the lower surface of the top plate 118 by a thinfilm 128 of infrared-transmissive adhesive material.

A modified photovoltaic module 130 according to a sixth embodiment ofthe present invention is schematically illustrated in the sectionalelevational view of FIG. 10. As in the case of the first embodiment ofthe modified photovoltaic module 30 illustrated in FIG. 5, the modifiedphotovoltaic module 130 of this sixth embodiment includes a solar cellstack 132 fitted with external current-collecting electrodes 134 forconnecting the solar cell stack 132 to an external load. Further, thesolar stack 132 is encapsulated on its upper surface by an outer layerof upper surface encapsulant resin 136, and on its lower surface by aninner layer 140 of lower surface encapsulant resin. In addition, theupper surface encapsulant resin layer 136 is covered with a top plate138, and the lower surface encapsulant resin layer 140 is covered by abacking plate 144. In this embodiment of the present invention, aninfrared-transmissive overlay film 146 is embedded in the upper surfaceencapsulant resin layer 136. The overlay film 146 is provided with athree-dimensional pattern simulating the appearance of roofing granuleson a conventional roofing shingle. In addition, the overlay film 146includes pigment that absorbs radiation in the visible range, providinga hue simulating the hue of a conventional roofing shingle.

A modified photovoltaic module 150 according to a seventh embodiment ofthe present invention is schematically illustrated in the sectionalelevational view of FIG. 11. As in the case of the first embodiment ofthe modified photovoltaic module 30 illustrated in FIG. 5, the modifiedphotovoltaic module 150 of this seventh embodiment includes a solar cellstack 152 fitted with external current-collecting electrodes 154 forconnecting the solar cell stack 152 to an external load. Further, thesolar stack 152 is encapsulated on its upper surface by an outer layerof upper surface encapsulant resin 156, and on its lower surface by aninner layer 160 of lower surface encapsulant resin. In addition, theupper surface encapsulant resin layer 156 is covered with a top plate158, and the lower surface encapsulant resin layer 160 is covered by abacking plate 164. In this embodiment of the present invention, theupper surface encapsulant resin layer 156 has a decorative pigment 166dispersed therein to simulate the appearance of a conventional roofingshingle.

FIG. 12 is a schematic, sectional elevational view of another embodimentof the photovoltaic module 200 of the present invention. In thisembodiment, the photovoltaic module 200 includes a solar cell stack orphotovoltaic element 212 having an upper surface 215. The solar cellstack 212 is fitted with external current-collecting electrodes 214 forconnecting the photovoltaic element 212 to an external load (not shown).In this embodiment, an encapsulant resin layer 216 covers over the uppersurface 215 of the photovoltaic element 212, and a decorative overlay226 is positioned above the upper surface 215 of the photovoltaicelement 212, and in particular in this embodiment, outside theencapsulant resin layer 216. The overlay 226 is substantiallytransmissive of near infrared radiation and infrared radiation. In thealternative, the decorative overlay can be positioned under theencapsulant resin layer 216 (not shown) or embedded in the encapsulantresin layer 216 (not shown). Further, the solar stack 212 isencapsulated on its lower surface by an inner layer 220 of lower surfaceencapsulant resin. In addition, the lower surface encapsulant resinlayer 220 is covered by a backing layer 224. In this embodiment of thepresent invention, the decorative overlay 226 simulates the appearanceof a conventional roofing tile.

The decorative overlay can be formed using a conventional CMYK printingprocess. Alternatively, specific inks or coating compositions can beselected for the purpose of better reproducing a chosen image or design.The decorative overlay can be formed using a single ink or coloredcoating composition, or by two or more inks or colored coatingcompositions. Preferably, the inks or coating compositions are selectedfrom materials that are substantially infrared-transmissive.

In one aspect of the present invention, the decorative overlay isdiscontinuous and includes a first portion which is free from anycoating material (“cutout portion”) whatsoever and a second portionincluding coating material. The cutout portion can be maximizedconsistent with the design objectives of the decorative overlay in orderto minimize any possible reduction in the electrical output from thephotovoltaic elements associated with the use of the overlay.

In another aspect of the present invention, the decorative overlayincludes a first portion which is free from any pigment material(“unpigmented portion”) and a second portion including pigment material.The unpigmented portion can similarly be maximized consistent with thedesign objectives of the decorative overlay in order to minimize anypossible reduction in the electrical output from the photovoltaicelements associated with the use of the overlay.

Solar stacks or photovoltaic elements that can be employed in theimproved photovoltaic modules of the present invention can include oneor more semiconductor photoactive layers of any type known in the art,such as, for example, semiconductor single crystal silicon layers,non-single crystal semiconductor silicon layers such as amorphoussemiconductor silicon layers, microcrystalline semiconductor siliconlayers, nanocrystalline semiconductor silicon layers, polycrystallinesemiconductor silicon layers, and compound semiconductor layers. Thephotoactive semiconductor silicon layers can be stacked, and thejunctions between the stacked layers can be of the pn-type, the np-type,the Schottky type, etc. The photoactive layers can include an n-typesilicon layer doped with an electron donor such as phosphorous, orientedtowards incident solar radiation, and a p-type silicon layer doped withan electron acceptor, such as boron. The semiconductor stacks caninclude transparent electrical current conducting layers formed fromelectrically conductive semiconductor materials such as indium oxide,stannic oxide, zinc oxide, titanium dioxide, cadmium stannate, and thelike.

The present invention can also employ thin film-type photovoltaicmaterials, such as multi-junction amorphous silicon solar cells producedon thin, flexible stainless steel substrates and available from UnitedSolar Ovonic LLC, Auburn Hills, Mich., which can be encapsulated inUV-stabilized polymers such as ethylene-vinyl acetate copolymers andfluoropolymers such as Tefzel (ethylene-tetrafluoroethylene)fluoropolymer available from Du Pont de Nemours. Thin film photovoltaicmaterials employing organic semiconductor materials can also be used.

Resins suitable for use in the present invention for encapsulatingsemiconductor photovoltaic elements include ethylene vinyl acetatecopolymer resins, ethylene ethyl acrylate copolymer resins, ethylenemethyl acrylate copolymer resins, polyvinyl butyral resins, polyurethaneresins, fluororesins, and silicone resins. Resins that are substantiallytransparent or at least transmissive to near infrared radiation and toinfrared radiation, such as ethylene vinyl acetate resins, arepreferred. The resins can be employed in the form thermoplastic orthermosetting fluids applied to a substrate including the photovoltaicmaterials, as films applied to the photovoltaic materials, or the like.

The physical properties of encapsulant resins for use in preparing thephotovoltaic modules of the present invention can be adjusted byselecting resins having suitable average molecular weight, suitablemolecular weight distributions, suitable degrees of branching, andsuitable levels of crosslinking. Preferably, the physical properties ofthe encapsulant resin are chosen to provide suitable impact resistance,low temperature resistance, high temperature resistance, environmentalstability, and adhesion for use in encapsulating semiconductorphotovoltaic elements in photovoltaic modules for exterior use.

The encapsulant resins used in preparing the photovoltaic modules of thepresent invention can include suitable amounts, preferably from about0.1 to 1.0 percent by weight of the encapsulant resin, of additives toenhance the ultraviolet radiation resistance and/or the radiationstabilization of the encapsulant resin. For example, ultravioletradiation absorbers such as benzophenones, benzotriazoles,cyanoacrylates, and salicylic acid derivatives can be employed,including 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-n-octyloxybenzophenone,2-(2-hydroxy-5-t-octylphenyl)benzotriazole, titanium dioxide, cerium(IV) oxide, zinc oxide and stannic oxide. Preferred ultravioletradiation absorbers include nanoparticle zinc oxides and titaniumdioxides. Suitable radiation stabilizers, which are to be used inconjunction with ultraviolet radiation absorbents, include hinderedamine bases such as, for example, derivatives of 2,2,6,6-tetramethylpiperidine of lower molecular weight or in polymeric form. Theencapsulant resins can also include antioxidants such as hinderedphenols, and adhesion-promoting agents such as organic titanates.

The optional top plate or cover member used for preparing thephotovoltaic modules of the present invention is preferably formed froma material which is substantially transparent to near infrared radiationand infrared radiation, and has good mechanical strength. Suitablematerials include tempered glass sheets having high transparency to nearinfrared and infrared radiation, and synthetic polymer sheets and filmssuch as fluororesin sheets and films, and acrylic sheets and films.Suitable fluororesins include polyvinylidene fluoride resins andtetrafluoroethylene-ethylene copolymers. When a synthetic polymer filmis employed as a cover member, the cover member preferably has athickness of from about 10 to 100 micrometers.

In some embodiments of the photovoltaic module of the present invention,the encapsulant resin can include a visible light-absorbing colorant,such as a dye or pigment. Preferably, when such a visible lightabsorbing colorant is included in the encapsulant resin, the colorant isselected to have high transmissivity to near infrared radiation andinfrared radiation.

In the photovoltaic module of the present invention, the lower surfaceencapsulant resin may be the same resin as employed as the upper surfaceencapsulant resin. However, the lower surface encapsulant resin can alsodiffer from the resin used as upper surface encapsulant resin, in thatthe service requirements differ for these two resin layers. Inparticular, the lower surface encapsulant resin need not be transmissiveto near infrared radiation and infrared radiation. Thus, in addition tothe resin materials that can be employed for forming the upper surfaceencapsulant resin layer, other resin materials, such as epoxy resins,can be used to form the lower surface encapsulant resin layer.

The backing plate employed in preparing the photovoltaic modules of thepresent invention is preferably formed from a rigid material, such asaluminum, steel, or a reinforced composite material, and more preferablya rigid electrically insulating material having low electricalconductivity, such as a nylon, a polytetrafluoroethylene material,polycarbonate, polyethylene, polystyrene, polyester, or the like.However, more flexible, less rigid materials may also be employed.

Preferably, in the photovoltaic modules of the present invention a colorlayer is selected such that, despite its pigmentation, it does notprevent the passage of the wavelengths within the solar spectrum thatare largely responsible for the photovoltaic activity.

The present invention also provides a method of producing a photovoltaicmodule having controllable and desirable aesthetics for use in roofapplications while still maintaining sufficient efficiency in powergeneration. In the process of the present invention an overlay film orcoating having a desirable visual appearance in the visible range of thespectrum, and substantially transmissive of near infrared and infraredradiation is applied to or incorporated in a photovoltaic device. Thephotovoltaic device is capable of producing electricity because nearinfrared and infrared radiation passing through the overlay film orcoating activate the photovoltaic device.

In one embodiment, the coating or film is transmissive or transparent inthe near infrared range and scatters, reflects or absorbs light in thevisible range of the spectrum to produce a desired appearance.Infrared-transmissive pigments can be used to provide visible color tothe coating or film. Suitable infrared-transmissive pigments can beinorganic or organic. In the case of organic pigments, it is preferredto include a protective overlay film that contains an ultravioletabsorber. The ultraviolet absorber provides an element of weatherabilityenhancement for organic transparent pigments. Examples ofinfrared-transmissive pigments that can be employed in the photovoltaicmodules of the present invention include zinc sulfide, zinc oxide,nanoparticle titanium dioxide and other nanopigments, CI Pigment Black31, CI Pigment Black 32, CI Pigment Red 122, CI Pigment Yellow 13,perylene pigments, ultramarine blue pigments, quinacrodone pigments, azopigments, and pearlescent pigments.

Preferred polymers for such films include acrylics, polycarbonates andfluoropolymers such as fluororesins. Ultraviolet radiation resistantpolymers such as acrylic polymers and fluoropolymers are especiallypreferred.

In one embodiment, a continuous coating or film is provided over theentire surface of the photovoltaic module. In another embodiment, thecoating or film is discontinuous. Such discontinuous coatings can beapplied by printing techniques. Coloration to produce the desiredappearance can be accomplished by a three- or four-color halftoneprinting process where different portions or dots are printed withdifferent colors to provide an overall visual effect when viewed from adistance. In some instances, monochromatic prints can also be employedwhere the base background color of the photovoltaic module itself alsocontributes to the overall color and appearance of the modified moduleof the invention.

In the case of a discontinuous coating, some of the printed areas canoptionally be opaque even to near infrared or infrared radiationprovided a sufficient area of the photovoltaic surface is available tocapture light to activate the device. Such opacity in selected portionsof the surface can be used to expand the range of accessible aestheticeffects for the photovoltaic module in a roofing application.

The use of infrared-transmissive pigments to modify the surface ofphotovoltaic modules greatly improves the ability to harmonize suchmodules in an aesthetically pleasant fashion with the rest of theroofing cover while, also eliminating the narrow color selection issueposed by the products currently available.

EXAMPLE

A photovoltaic cell was connected to a Simpson 260 volt meter andexposed to sky light on a sunny day with an ambient temperature of 24 C.The voltage reading for the output of the photovoltaic cell was 8.3 V.The visual appearance of the photovoltaic cell was unchanged from itsnatural condition.

A sheet of infrared long-pass film having a high transmissivity in thenear infrared region of the spectrum and strong absorbance in thevisible spectrum was placed over the exposed surface of the photovoltaiccell. The voltage reading for the output of the photovoltaic cell was7.8 V. The photovoltaic cell was completely obscured by the infraredlong-pass film and the surface had a black appearance. The electricaloutput of the photovoltaic cell remained at 94% of its natural levelwithout the infrared-transmissive overlay.

Various modifications can be made in the details of the variousembodiments of the processes and articles of the present invention, allwithin the scope and spirit of the invention and defined by the appendedclaims.

The invention claimed is:
 1. A process for producing a decorativephotovoltaic module comprising: (a) providing a photovoltaic moduleincluding a semiconductor stack encapsulated in an infrared-transmissiveresin having an upper resin layer, and (b) adhering an overlay filmbearing a decorative pattern to the upper resin layer using aninfrared-transmissive adhesive material, wherein the decorative patternfurther includes an infrared-transmissive ink on at least a firstportion of the upper resin layer and an opaque ink on at least a secondportion of the upper resin layer.
 2. A process according to claim 1wherein the at least one infrared-transmissive pigment is selected fromthe group consisting of zinc sulfide, zinc oxide, nanoparticle titaniumdioxide, CI Pigment Black 31, CI Pigment Black 32, CI Pigment Red 122,and CI Pigment Yellow
 13. 3. The process of claim 1, wherein thedecorative photovoltaic module is incorporated into a roofing cover. 4.A process according to claim 1 wherein the decorative overlay simulatesthe appearance of a conventional roofing shingle surface.
 5. A processaccording to claim 1 wherein the decorative layer is formed by ahalftone printing process.